I’m running an ET-2720 and had a similar issue (magenta and cyan were very faing and the yellow print head stopped working at all). Power cleaning solved the issue. From the manual:
Power Cleaning
If you still see white or dark lines or missing nozzles in your printouts, even after cleaning the print head several times, you can run a Power Cleaning. If you do not see improvement after running a Power Cleaning, turn off the product and wait at least 12 hours before running another Power Cleaning.
Caution: Running a Power Cleaning consumes a lot of ink, so you should run it only if necessary. Make sure each ink tank is at least one-third full before running a Power Cleaning, or it may damage the product.
Caution: Power Cleaning may cause the ink pads to reach their capacity sooner. When an ink pad reaches the end of its service life, the product stops printing and you must contact Epson for support.
I had to top off all of the ink compartments - 1/3 full didn’t even come close. It’s a little complex - complete details on the procedure are available online or in your manual.
Good Luck
Lucy